Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P7/00—Resonators of the waveguide type
  • H01P7/005—Helical resonators; Spiral resonators

Definitions

• the present invention relates to a resonator assembly comprising a helix resonator consisting of a conductor wound as a cylindrical coil, and a housing at least partly made of conductive material and enveloping the helix resonator.
• the present invention relates primarily to resonators used in filters of mobile telephone systems, although the invention can also be utilized in other contexts. Hereinafter, however, the invention will be described by way of example particularly with reference to mobile telephone systems.
• a straight quarter wave resonator is previously known comprised of a straight conductor inserted into a metal housing. Such a resonator is suited for use in filters of mobile telephone system, for example.
• GSM Global System for Mobile communications
• a quarter wave coaxial reso- nator is about 80 mm long.
• a resonator of the size described above has turned out to be too big.
• a solution for decreasing the resonator length has been to equip the resonator with a "cap" enabling the length of the straight part of the resonator to be decreased, based on the fact that the cap loads the resonator by lowering the frequency back to the 900 Mhz area.
• High capacitance between the cap and the resonator cavity causes the quality factor, i.e. Q factor, to drop sharply.
• a resonator assembly of this kind thus fails to produce high quality factors required by the resonators of base station filters, for example.
• a resonator called a helix resonator is also previously known comprising a quarter wave long resonator wound as a cylindrical coil.
• the resonator is then comprised of a conductor wound to form a coil of cylindrical form using thread or section wire.
• the helix resonator is inserted into a housing of conductive material serving as a ground plane, one end of the resonator being coupled thereto. The other end of the helix resonator is left open.
• the helix resonator is significantly smaller than a coaxial resonator with corresponding characteristics.
• the helix resonator suffers from the same problem, i.e. too low a quality factor, as the above-described straight coaxial resonator equipped with a cap.
• An object the present invention is to solve the problem described above and provide a resonator assembly having a high quality factor and tak- ing up a relatively small space.
• a resonator assembly of the invention comprising a helix resonator consisting of a conductor wound as a cylindrical coil, and characterized by the conductor that forms said cylindrical coil continuing as a straight conductor part, which extends from the cy- lindrical coil substantially in the direction of the longitudinal axis of the cylindrical coil, whereby said straight conductor part constitutes a coaxial resonator, and said housing enveloping the resonator formed by a combination of the helix resonator and the coaxial resonator.
• the invention is based on the idea that combining a helix resonator and a straight coaxial resonator into one resonator provides a resonator assembly having significantly better characteristics than the known resonators.
• the conductor forming the coil of the helix resonator can continue as a straight conductor part constituting a coaxial resonator, in other words the conductor can be the same physical wire whose first end is shaped as a spiral and whose second end is shaped as a straight conductor part.
• the conductors can be two separate wires coupled with each other in a manner known per se, for example by soldering.
• one wire is shaped as a spiral and the other as a straight conductor part.
• Practical experiments show that a resonator assembly comprised of a helix resonator and a straight coaxial resonator significantly enables space to be saved since the total length of the resonator assembly can thus be decreased, compared with the known straight coaxial resonator, without the quality factor, i.e. Q factor, of the resonator consequently being significantly lowered.
• the most significant advantage of the resonator assembly of the invention is that it is space-efficient without the resonator quality factor consequently being lowered.
• the resonator assembly of the invention is suited for use in RF filters, for example.
• the diameter of the conductor forming the helix resonator is different from the diameter of the conductor part forming the coaxial resonator.
• This embodiment of the invention enables an impedance change to take place at the joining point of the conductors where the diameter changes. Hence, a necessary impedance change in the assembly used can be provided by means of dimensioning.
• the preferred embodiments of the resonator assembly of the invention are disclosed in the attached dependent claims 2 and 3. In the following, the invention will be described in closer detail by way of example with reference to the accompanying drawings, in which Figure 1 shows a first preferred embodiment of a resonator assembly in accordance with the invention, and
• Figure 2 shows a second preferred embodiment of the resonator assembly of the invention.
• Figure 1 shows a first preferred embodiment of a resonator assem- bly in accordance with the invention.
• the resonator assembly of Figure 1 is assumed to be a resonator assembly used in an RF filter of a GSM system.
• the resonator assembly shown in Figure 1 comprises a helix resonator 2 connected directly to a coaxial resonator 3.
• the helix resonator 2 is comprised of wire wound as a cylindrical coil, the diameter of the wire being for example 4 to 8 mm. Suitable wire materials include silver-coated aluminum, copper or steel.
• a dash line 7 in Figure 1 illustrates the longitudinal axis of the cylindrical coil.
• the wire continues from the lower part of the cylindrical coil as a straight conductor part 3 projecting from the cylindrical coil substantially in the direction of the longitudinal axis 7 thereof.
• the conductor part 3 thus constitutes a straight coaxial resonator.
• the total height of a resonator assembly 1 can be 40 to 50 mm, for example, in which case the straight resonator 3 accounts for approximately 18 mm while the helix resonator 2 accounts for approximately 20 to 30 mm.
• Such dimensioning enables almost as high a quality factor as obtained by means of an 80-mm-long straight coaxial resonator.
• the resonator assembly 1 of Figure 1 thus comprises the resonator comprising the helix resonator 2 and the straight coaxial resonator 3 coupled to each other.
• the resonator is arranged in a housing 4 at least partly made of conductive material.
• at least the inner surface of the housing 4 should be of conductive material.
• the housing 4 can be made of aluminum with an inner surface coated with silver.
• the housing In order to couple an input conductor 5 to the resonator at a coupling point 8, the housing has an opening arranged therein. Signals to be filtered are fed to the resonator through the conductor 5.
• the impedance of such an assembly is approximately 50 ⁇ , and approximately 200 ⁇ or more at an open top end 6 of the resonator.
• the resonator assembly of Figure 1 can effect an impedance change by using conductors with different diameter lengths in the helix resonator 2 and the straight coaxial resonator 3.

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• 1998
  • 1998-04-24 FI FI980911A patent/FI980911A/sv unknown
• 1999
  • 1999-04-21 JP JP2000546412A patent/JP2002513228A/ja active Pending
  • 1999-04-21 AU AU36079/99A patent/AU756013B2/en not_active Ceased
  • 1999-04-21 EP EP99918005A patent/EP1074059A1/en not_active Withdrawn
  • 1999-04-21 CN CNB998052884A patent/CN1136626C/zh not_active Expired - Fee Related
  • 1999-04-21 WO PCT/FI1999/000322 patent/WO1999056340A1/en not_active Application Discontinuation
  • 1999-04-21 US US09/673,764 patent/US6456175B1/en not_active Expired - Fee Related
• 2000
  • 2000-10-23 NO NO20005333A patent/NO20005333D0/no not_active Application Discontinuation

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